In a pulp mill, fluffed, flash dried pulp is compressed into slabs in a slab press. Several slabs are compressed one on top of another and then discharged in a stack of slabs which are further compressed and then packaged to form a bale for shipment. A stack of slabs, generally at least three slabs, is discharged from a slab press and deposited onto a conveyor. The stack of three slabs is then conveyed to a bale press, which compresses all three slabs in the stack together to form a bale. The bale is then packaged for shipment.
A typical slab from a slab press weighs approximately 250 kilograms and 600 mm by 800 mm with varying heights. The cycle time to make an individual slab in a slab press results in a low production rate, therefore the slab press forms as many large slabs as possible, one on top of the other, before discharging because the step of discharging a stack of slabs onto a conveyor causes a delay in the production of slabs. For this reason, three or even four slabs are produced in one cycle in order to maximize the production rate. However, when a stack of three or four slabs are placed on a conveyor the height of the stack is often greater than is desired for packaging into a bale, or greater than required by customers, and therefore it is necessary to remove one or more slabs from the top of the stack and combine the removed slabs with other slabs so that stacks of slabs passing to a bale press have fewer slabs than the stack of slabs exiting from the slab press.
Whereas one could produce less slabs in a stack leaving a slab press, this would decrease the production rate of slabs and can cause a bottleneck in the production of pulp. For instance, if one was to produce only two slabs of identical height instead of three slabs of the same height per stack from a slab press, then the time to discharge a stack with only two slabs results in a production rate loss as high as 20%.